Just thinking about how Ed's automail hurts whenever the weather changes. Not just day to day weather but in extremes, like gloomy rainy days. Or hot humid heat. Either way his ports hurt and body aches.
In the cold the metal starts to freeze and brings down his own body Temperature, along with the fact that metal contracts when cold. His ports would get to tight to walk or move comfortably. Since he's always cold, his immune system goes down and he gets sick more frequently. Frost bite being another big possibility.
In the heat he suffers just as much, his automail heating up and thus the ports heat up his skin making him more susceptible to hypothermia, even heatstrokes and heat rashes (hyperthermia when it gets cold) ,even burning him at times.
Both sides of the coin can also potentially damage his automail. The condensation from the humid heat and the water from frost and snow can lead to the possibility of it rusting his joints and making his automail weaker in combat. Making his reaction time slower due to the bolts and hinges not moving properly.
All these reasons gave me the idea that resembool is the perfect place for him and his automail. The weather doesn't really change, only during rare times of a rainstorm or an unusually hot summer but overall it's a place that's constant. Kinda how Winry is a constant for Ed, with everything else being so hectic and unsure ( the homunculus, the government, foreign royalty, even the possibility of them not being able to get their bodies back) winry and resembool are the things that Ed knows for sure are waiting for him.
It's also where he first was fitted with his new arm and leg. He did his recovery there and so his body has essentially healed and adjusted to the areas conditions. I mean anytime he and Al need to rest or take a break it's usually at resembool, sure it may be for matienence but they feel most at peace there.
